The present invention relates to a process and an apparatus for inspecting junctions in sleeve lining fabrics for the manufacture of toothed belts, each sleeve having a substantially cylindrical textile reinforcing layer embedded in at least one layer of elastomeric material shaped so as to define, in said sleeve, an toothed surface on its inner periphery provided with a number of shaped teeth extending parallel to the axis of the sleeve. The teeth are spaced apart from each other by a predetermined pitch, a fabric lining being applied to said toothed surface, said lining having at least two end edges joined by a seam extending longitudinally in the sleeve.
It is known that driving belts are essentially comprised of an inextensible textile layer of substantially cylindrical structure embedded in at least a layer of elastomeric material such shaped as to define a toothed inner surface. In many cases, a fabric lining is applied to the inner toothed surface and it has the double function of reinforcing the individual teeth by enhancing the bending strength thereof and protecting the elastomeric material from external agents with which the belt may be brought into contact, once it has been placed in use.
Belts of the above type are obtained from a slitting operation carried out according to a number of axially spaced circumferential lines on an axially elongated tubular cylindrical sleeve having a toothed inner surface.
For the manufacture of this sleeve a tubular body made of stretch fabric is first slipped onto a cylindrical matrix provided with longitudinal grooves the shape of which matches the shape of the teeth. This tubular body, designed to form said fabric lining, is substantially formed with one or more lengths of rubberized fabric the end edges of which are disposed close to each other and joined by at least one connecting seam extending longitudinally to the resulting tubular body.
Then at least one reinforcing layer of inextensible textile material is wrapped around the textile tubular body fitted on the matrix and at least one layer of uncured elastomeric material is subsequently placed over the reinforcing layer. The semifinished product thus obtained is submitted to a vulcanization process in an autoclave.
During this operation the semifinished product, after being engaged in a coating sheath made of rubber, undergoes a suitable heating by steam under pressure which is sent to the inside of the matrix and the outside of the sheath which surrounds the semifinished product.
By the effect of the steam pressure acting on said coating rubber sheath through homogeneously distributed centripetal forces the elastomeric material is forced to pass through the inextensible textile fibers so that it fills the grooves of the matrix thereby creating the inner toothing of the sleeve. During this step the part of the lining fabric which is impervious to the elastomeric material is pushed into the grooves and perfectly mates with the matrix surface.
Therefore when the vulcanization is over the lining fabric will be located directly on the inner surface of the finished sleeve and will be able to perform the above mentioned functions in the belts to be obtained from the sleeve by the circumferential slitting of the sleeve after removing the sleeve from the matrix.
As a result of the above process it is noted that the thrust action exerted by the elastomeric material during the vulcanization process in some cases can give rise to the separation from each other of the end edges of the lining fabric in the junction area.
It can be easily understood that such a detachment can give rise to the complete loss of operating features of the fabric lining. In fact external agents such as chemicals or other agents can easily damage the elastomeric material through any open junction areas, which can bring about a quick deterioration of the belt and the consequent breakage of it.
The presence of separation areas between the end edges of the fabric can also involve an unacceptable weakening of the bending strength of the tooth on which the junction is located.
It is also to be pointed out that in many applications the junction or junctions must have a predetermined positioning on the tooth outline. In fact if the junction is positioned at particular locations on the tooth outline, such as for example on one of the tooth flanks, it could give rise to an undesirable reduction in the resistance to bending stress of the tooth even if it has been correctly made.
In addition, under this situation the junction would be submitted to high stresses that could cause the separation of the fabric edges while the belt is being used.
It is apparent that the above described situations bring about high risks of breakage of the belt in use, which must be absolutely avoided.
The methods currently adopted in an attempt to restrain said risks as much as possible are essentially based on the performance of quality inspections carried out by an operator who merely visually observes the toothed surface of the sleeve or the belts subsequently obtained.
It can be easily understood that these empirical inspection methods are not very reliable, since the identification of possible anomalies in the lining fabric junctions depends to a great extent on the skill of the operator entrusted with this inspection and the care he or she takes in carrying out the operation.
In this connection it is also necessary to consider the fact that visual identification of possible separations between the seamed edges of the lining fabric is very difficult, since both the lining fabric and the elastomeric material appear generally black to the human eye.
In addition it must be born in mind that the inspection methods currently used do not allow timely interventions when the junctions have anomalies due to high speed running of the apparatus used during the sleeve manufacturing operations.